We got Hoppers on our past trip but mostly for Food & Wine and being interested in attending multiple Eat to the Beat concerts. If we hadn't been doing that, I'm not sure we would have needed them. The only other day we used them was our final day, when we went to MK for the last time, used up all of our FPs and felt "done" with that park, so we went back to Epcot for another pass at F&W. Even THAT might not have happened if not for F&W, since we only had about two hours there and we probably easily could have stuck around at MK or resort-hopped a bit more (we went to Boardwalk first before going to Epcot).
But if you trip is relatively short and you want to be able to go to be more spontaneous (say, you're ready for an MK break and omigosh there's a Soarin' FP available in an hour!), it's definitely worth it to have. I was ultimately glad we did, even though for the most part, we would have been able to stick to one park per day.